Data storage device

ABSTRACT

Provided are novel data storage devices, such as hard disk apparatuses. The devices include a clean chamber accommodating a component formed from a free cutting stainless steel. The free cutting stainless steel has a sulfur (S) content of not less than 0.25 percent by mass and a manganese-to-sulfur content ratio (Mn/S) of not greater than 1.8. The free cutting stainless steel has been subjected to: (1) an acid cleaning; (2) to a passivation treatment; (3) to a degreasing treatment and to a subsequent rust-removing, descaling chemical treatment; or (5) to a degreasing treatment and to a subsequent chromate treatment.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C.§119, of Japanese Application Nos. 09-343791, filed Nov. 28, 1997,09-343792, filed Nov. 28, 1997, 10-124095, filed Apr. 17, 1998 and10-295692, filed Oct. 16, 1998, the contents of each of said documentsbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a data storage device, such as ahard disk apparatus. The present invention also relates to a hard diskapparatus, which finds use as a main or auxiliary storage device of acomputer system.

[0004] 2. Description of the Related Art

[0005] Hard disk apparatuses generally have a clean chamber defined by abase member and a cover member, and one or more hard disks accommodatedin the clean chamber so as to be accessible by a magnetic head supportedby a head arm.

[0006] More specifically, at least a rotor hub of a spindle motor isrotatably received in the clean chamber, and one or more hard disks aremounted on the rotor hub. The clean chamber additionally accommodates ahead assembly which includes a voice coil motor. The voice coil motorserves to rotationally drive the head arm, such that the magnetic headon an end of the arm traces the surface of each disk to read and writedata.

[0007] In the hard disk apparatus of the type described above, the airinside the clean chamber must be maintained at a high degree ofcleanness in order to enhance the recording density and to prevent anycrush attributable to jamming of dust particles between the head and thedisk surface. This requires not only that the interior of the cleanchamber be shielded from the ambient air to prevent invasion by dust,but also that the generation of dust particles, or so-calledcontaminants, inside the clean chamber be suppressed.

[0008] Stainless steels, which are resistant to rusting as compared withordinary steels or structural steels, are most commonly used as thematerials for parts inside the clean chamber, such as the shaft and therotor hub of the spindle motor, the shaft and arm of the head assemblyand other elements, such as screws. The use of such stainless steels isintended mainly to satisfy the above-described requirements.

[0009] At the same time, a high degree of dimensional precision isrequired for parts of a precision machine or device, such as a hard diskapparatus. This, in turn, requires a high degree of workability of thematerial to be used. Among the various types of working techniques whichare available, cutting, i.e., machining, is most frequently employed.Free cutting steels, which contain various free cutting elements servingto improve cutting characteristic, i.e., machinability, are thereforefinding broadened use.

[0010] Although stainless steel in general is hard to machine,machinability can be improved by the addition thereto of free cuttingelements, such as sulfur (S), tellurium (Te), selenium (Se), etc.Stainless steel containing sulfur as a free cutting element at a contentof 0.25 percent by mass or greater is commonly used because of itsmoderate cost and good machinability. In this type of steel, sulfurexists primarily in the form of manganese sulfide (MnS). Themanganese-to-sulfur content ratio Mn/S is usually set at about 4, inconsideration of stability in production and ease of machining.

[0011] The above-described stainless steel is, thus, rich in sulfur,which is added for the purpose of improving machinability, and ispresent primarily in the form of manganese sulfide. There is, however, arisk that manganese sulfide will generate a corrosive hydrogen sulfide(H₂S) gas upon reaction with the moisture in atmospheric air. For thisreason, ordinary stainless steels having an Mn/S ratio of about 4 arenot suitable for use as the material for parts of a hard disk apparatusin a hermetic clean chamber.

[0012] In contrast, stainless steels having an Mn/S ratio not greaterthan 1.8 are substantially free of generation of sulfur-containinggases. Such smaller value of the Mn/S ratio, i.e., a smaller Mn content,reduces the tendency of formation of the chemically active manganesesulfide. Instead, the formation of chromium sulfide (CrS), which is morestable than manganese sulfide, is enhanced.

[0013] Stainless steels having an Mn/S ratio not greater than 1.8,however, tend to rust. At the same time, they exhibit a higher chemicalstability in wet environments. In addition, these stainless steels areliable to generate particles containing sulfur, which is intended toimprove machinability. This poses a risk of contamination by corrosiveparticles.

[0014] A stainless steel containing 0.25 percent by mass or greater ofsulfur as a free cutting element at a manganese-to-sulfur ratio Mn/S ofaround 4 may be subjected to a heat treatment, e.g., baking. This servesto forcibly release sulfur gas, thereby suppressing contamination. Inaddition, such a stainless steel may be passivation-treated to attainimproved corrosion resistance while allowing removal of particles. Aheat treatment as described above may be conducted after the passivationtreatment. Processes including such treatments, however, are notrecommended from the view points of yield and equipment cost.

[0015] It is also possible to employ a free cutting stainless steelhaving a sulfur content of 0.25 percent by mass or greater at amanganese-to-sulfur ratio Mn/S of 1.8 or less. This free cuttingstainless steel, however, also poses a problem when subjected to an acidcleaning conducted with an acid solution having an acid concentrationexceeding 15 percent by volume. In this regard, it permits thedissolution of free cutting grains rich in chemically stable CrS,thereby allowing the generation of H₂S.

[0016] Under these circumstances, it is an object of the presentinvention to provide a hard disk apparatus which suppresses thegeneration of sulfur-containing corrosive gas from stainless steel inthe clean chamber. This prevents a reduction in resistance to corrosionwhile preventing particle contamination caused by matter which may befreed from surfaces of the parts constructed of the stainless steel.

[0017] Other objects and advantages of the present invention will becomeapparent to one of ordinary skill in the art upon review of thespecification, drawings and claims appended hereto.

SUMMARY OF THE INVENTION

[0018] In accordance with one aspect of the present invention, providedis a hard disk apparatus. The apparatus comprises a clean chamberaccommodating a hard disk driven by a spindle motor, and a magnetic headcapable of making access to the hard disk. A free cutting stainlesssteel is used as the material of a member accommodated in the cleanchamber. The free cutting stainless steel has a sulfur (S) content ofnot less than 0.25 percent by mass and a manganese-to-sulfur contentratio (Mn/S) of not greater than 1.8. The free cutting stainless steelhas been subjected to an acid cleaning.

[0019] Preferably, the acid cleaning is conducted with an aqueoussolution of an acid capable of removing contaminants, rust and scaleremaining on the surface of the free cutting stainless steel. The acidcleaning is preferably conducted with a solution of nitric acid. Morepreferably, the free cutting stainless steel after the acid cleaning issubjected to a neutralizing treatment and further to a chromatetreatment.

[0020] Is accordance with a further aspect of the invention, a hard diskapparatus is provided which comprises a clean chamber accommodating ahard disk driven by a spindle motor, and a magnetic head capable ofmaking access to the hard disk. A free cutting stainless steel is usedas the material of a member accommodated in the clean chamber. The freecutting stainless steel has a sulfur (S) content of not less than 0.25percent by mass and a manganese-to-sulfur content ratio (Mn/S) of notgreater than 1.8. The free cutting stainless steel has been subjected toa passivation treatment.

[0021] Preferably, the passivation treatment is conducted with atreating solution which is nitric acid alone. Alternatively, thepassivation treatment can be conducted with a treating solution which amixture of nitric acid and sodium bichromate, followed by an alkalineutralizing treatment. The alkali neutralizing treatment is preferablyfollowed by a chromate treatment.

[0022] It is also preferred that the stainless steel be heat-treated toa temperature of from about 100° C. to about 200° C. after thepassivation treatment. Alternatively, the heat treatment may beconducted at a temperature of from about 70° C. to about 150° C. in avacuum or a substantially vacuum atmosphere after the passivationtreatment.

[0023] In accordance with a further aspect of the invention, a hard diskapparatus is provided which comprises a clean chamber accommodating ahard disk driven by a spindle motor, and a magnetic head capable ofmaking access to the hard disk. A free cutting stainless steel is usedas the material of a member accommodated in the clean chamber. The freecutting stainless steel has a sulfur (S) content of not less than 0.25percent by mass and a manganese-to-sulfur content ratio (Mn/S) of notgreater than 1.8. The free cutting stainless steel has been subjected toa degreasing treatment and to a subsequent rust-removing, descalingchemical treatment.

[0024] By reducing the manganese-to-sulfur content ratio (Mn/S) below1.8, the sulfur compound contained within the free cutting stainlesssteel stabilizes, and the sulfur-containing corrosive gas generated fromthe sulfur compound by reaction with moisture in the air is reduced. Theresistance to corrosion can thereby be improved. Because the freecutting component is almost free from dissolution by the acid treatment,the generation of the gas and particles can effectively be prevented.

[0025] The rust-removing, descaling chemical treatment should beconducted under such conditions that are effective to remove anycontaminant, rust and scale remaining on the surface of the free cuttingstainless steel part, thereby improving the resistance to corrosion. Therust-removing, descaling chemical treatment further should be conductedat gentle conditions so as to avoid dissolution of free cuttingcomponents contained in the free cutting stainless steel. This can beaccomplished by, for example, an aqueous solution of an acid having anacid concentration of 3 percent by mass or less, or by alkalielectrolytic cleaning. Preferably, the free cutting stainless steel partis subjected to a chromate treatment subsequent to the chemicalrust-removing and descaling treatment.

[0026] In accordance with a further aspect of the invention, a hard diskapparatus is provided which comprises a clean chamber accommodating ahard disk driven by a spindle motor, and a magnetic head capable ofmaking access to the hard disk. A free cutting stainless steel is usedas the material of a member accommodated in the clean chamber. The freecutting stainless steel has a sulfur (S) content of not less than 0.25percent by mass and a manganese-to-sulfur content ratio (Mn/S) of notgreater than 1.8. The free cutting stainless steel has been subjected toa degreasing treatment and to a subsequent chromate treatment.

[0027] As described above, by reducing the manganese-to-sulfur contentratio (Mn/S) below 1.8, the sulfur compound contained within the freecutting stainless steel stabilizes, improving the resistance tocorrosion. Additionally, the sulfur-containing corrosive gas generatedfrom reaction of the sulfur compound with moisture in air is reduced.

[0028] Moreover, as a result of chromate treatment, resistance tocorrosion may be improved regardless of the generation of thesulfur-containing corrosive gas and of the dissolution of the freecutting components from the sulfur compound. In such a case, it ispreferable to remove the oil or grease and acid scale caused bymachining in mechanical descaling prior to degreasing. The scale canthereby be removed from the surface of the steel material, and theresistance to corrosion may be further improved by the subsequentchromate treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The objects and advantages of the invention will become apparentfrom the following detailed description of the preferred embodimentsthereof in connection with the accompanying drawings, in which:

[0030]FIG. 1 is a plan view of an embodiment of a hard disk apparatus,with the cover device removed therefrom;

[0031]FIG. 2 is a sectional elevational view of the hard disk apparatusshown in FIG. 1;

[0032]FIG. 3 is a partly-sectioned elevational view of a rotor hub of aspindle motor, used as a sample in the Examples;

[0033]FIG. 4 is a table showing results of evaluation of the Examplesand Comparative Examples for one aspect of the invention;

[0034]FIG. 5 is a table showing results of evaluation of the Examplesand Comparative Examples for a further aspect of the invention; and

[0035]FIG. 6 is a table showing results of evaluation of the Examplesand Comparative Examples for further aspects of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0036] Exemplary aspects of the present invention will be now bedescribed with reference to the drawing figures. While the invention isdirected to data storage devices in general, the following exemplaryaspects of the invention will be described with reference to a hard diskapparatus. FIG. 1 is a schematic plan view of a hard disk apparatus witha cover member part being removed therefrom. FIG. 2 is a sectional viewof the same.

[0037] The hard disk apparatus has a clean chamber defined by a basemember 2 and a cover member 4 covering the base member 2. The internalspace 6 of the clean chamber is hermetically sealed against the ambientair, so that clean atmosphere is maintained inside the clean chamber. Atleast one hard disk 8 (two disks shown in the illustrated embodiment)having a central hole is disposed in the internal space 6 of the cleanchamber in such a manner as to be rotationally driven by a spindle motor10.

[0038] The spindle motor 10 has a shaft 12 provided on the base member2, a cup-shaped rotor hub 16 rotatably supported on top of the shaft 12through a pair of bearings 14, and a stator 20 fixed to a lower portionof the shaft 12 so as to face rotor magnets 18 on the rotor hub 16across a small gap. The shaft 12 is fixed to and supported by the covermember 4, by means of a screw which is screwed into the upper end of theshaft 12. The hard disks 8, with the brims of their central holesfitting on the rotor hub 16, are fixed to the rotor hub 12 by means of aclamp member 24, with a spacer 22 intervening therebetween.

[0039] The inner space 6 of the clean chamber also receives a headassembly 26. The head assembly 26 has a plurality of pairs of head arms30 (two pairs shown in the illustrated embodiment) swingably supportedby a pivot shaft 28 fixed to the base member 2, magnetic heads 32secured to ends of the respective head arms 30, and a voice coil 34provided on the base ends of the head arms 30.

[0040] The arrangement is such that, when the voice coil 34 iselectrically energized, the head arms 30 are caused to oscillate withrespect to upper and lower stationary yoke plates 36, such that eachmagnetic head traces the surface of the associated hard disk 8 to writeand read data in and from the hard disks 8.

[0041] As described above, the internal space 6 of the cleaning chamberaccommodates various components, such as the spindle motor 10 fordriving the hard disks, as well as head assembly 26 for driving andcontrolling the magnetic heads 32 which trace the surfaces of the harddisks 8. There are internal parts and components made of a stainlesssteel, such as the rotor hub 16, shafts 12, 28, etc. These parts orcomponents, referred to as stainless-steel parts, are constructed of afree cutting stainless steel.

[0042] The free cutting stainless steel has a sulfur (S) content of 0.25percent by mass or greater and, hence, exhibits superior machinability.Sulfur as the element for enhancing machinability is present in the formof manganese sulfide (MnS) in the free cutting stainless steel. Themanganese-to-sulfur ratio (Mn/S) is set to be 1.8 or less, preferably1.5 or less. Thus, the content of chemically active manganese sulfidecan be maintained at a low level so as to restrain the stainless steelfrom generating sulfur-containing gases.

[0043] 1. Acid Cleaning of Free Cutting Stainless Steel

[0044] In accordance with a first aspect of the invention, the freecutting stainless steel which has been prepared to meet theabove-described requirements is machined into a desired shape and isthen subjected to an acid cleaning which is conducted with an aqueoussolution of an acid, such as nitric acid, whereby the surface of themachined stainless steel part is cleaned. More specifically, thisdegreasing treatment effectively serves to remove chlorine and sulfurtransferred from the machining oil during the machining, and scalegenerated during the machining, as well as micro-fine grains of freecutting components such as manganese sulfide. Thus, the corrosionresistance peculiar to the stainless steel material can be fullyutilized and contamination by particles can effectively be avoided.

[0045] The acid cleaning may, alternatively, be conducted using otheracidic solutions than that described above. This is provided that theacidic solution is effective to remove contaminants, scale and freecutting elements from the surface of the free cutting stainless steel.For example, it is possible to use an aqueous solution of sulfuric acid,hydrochloric acid or hydrofluoric acid.

[0046] The stainless steel which has undergone the above-described acidcleaning exhibits improved corrosion resistance and can prevent particlecontamination. When a further improvement in the corrosion resistance isdesired or required, the stainless steel which has undergone the acidcleaning may also be subjected to an alkali neutralizing treatment and asubsequent chromate treatment. As a result, an oxide film is forciblyformed on the surface of the stainless steel, thereby enhancingremarkably the corrosion resistance.

[0047] Advantages of the above-described aspects of the presentinvention can be further appreciated in light of the following examples.

EXAMPLE 1

[0048] An 18 Cr stainless steel, having a sulfur content of 0.3 percentby mass and a manganese content of 0.4 percent by mass (Mn/Sratio=1.33), was prepared. This stainless steel was machined to formsamples of a rotor hub 40 shown in FIG. 3, i.e., the rotor hub whichforms part of a spindle motor and which is to be accommodated in theclean chamber of a hard disk apparatus.

[0049] Each sample of the rotor hub 40 thus formed was subjected to analkali degreasing treatment and was then subjected to a 40-minute acidcleaning conducted with a 10 percent by volume aqueous solution ofnitric acid at 50° C., followed by rinsing with water, pure hot waterand pure water and a subsequent hot-air dehydration. A silver plate(stainless steel sheet plated with silver) was wound around each samplerotor hub thus obtained. The rotor hub together with the silver platewas wrapped in an aluminum foil and was shelved for 4 hours at 120° C.The silver plate was next taken out of the container for visualobservation of the degree of discoloration (silver plate color test).

[0050] Twenty (20) pieces of such rotor hub samples, having undergonethe acid cleaning treatment, were shelved for 360 hours in an 80° C.atmosphere of 90% humidity. Each piece of rotor hub was then subjectedto optical microscopic observation for any rusting.

[0051] A conductive tape was brought into contact with the surface ofeach of three pieces of the sample rotor hubs which had undergone theacid cleaning, descaling chemical treatment. Fifty (50) arbitrarilyselected particles of foreign matter transferred to the tape wereanalyzed through a scanning electron microscope/energy distributionX-ray analyzer (SEM/EDX), for the purpose of investigating the number ofsulfur-containing particles.

[0052] The results of this evaluation are summarized in line a) of thetable shown in FIG. 4. As used in the table, the “Number of rustingsamples” means the number of rotor hubs among the 20 sample pieces whichwere found to be rusty. The “Number of sulfur-containing particles,” asused in the table, refers to the number of particles among the 50arbitrary particles of foreign matter sampled which were found to berusty.

EXAMPLE 2

[0053] Sample rotor hubs prepared in Example 1 were subjected to analkali degreasing treatment and then to a 40-minute acid cleaningconducted with a 5 percent by volume aqueous solution of nitric acid at50° C. The sample rotor hubs were then rinsed with water, hot pure waterand pure water, followed by dehydration with hot air. The sample rotorhubs thus treated were evaluated to obtain the results shown in line b)of the table of FIG. 4.

EXAMPLE 3

[0054] Sample rotor hubs prepared in Example 1 were subjected to analkali degreasing treatment and then to a 3-minute acid cleaningconducted with a mixed acid solution containing 10 percent by volumenitric acid and 2 percent by volume fluoric acid. The sample rotor hubswere then rinsed with water, hot pure water and pure water, followed bydehydration with hot air. The sample rotor hubs thus treated wereevaluated to obtain the results shown in line c) of the table of FIG. 4.

COMPARATIVE EXAMPLE 1

[0055] Rotor hubs prepared as in Example 1 were directly subjected tocleaning with methylene chloride and a subsequent water rinse with theaid of a neutral detergent, without being subjected to acid cleaning.The rotor hubs thus treated were evaluated in the same manner as theExamples to obtain the results shown in line d) of the table of FIG. 4.

EXAMPLE 4

[0056] The sample rotor hubs prepared in Example 1 were immersed for 30minutes in a 20 percent by volume aqueous solution of sodium hydroxideat 80° C., and then subjected to a chromate treatment conducted byimmersing the rotor hubs in a 5 percent by weight aqueous solution ofsodium bichromate at 70° C. for 30 minutes. Evaluation was conducted inthe same manner as the preceding Examples to obtain the results shown inline e) of the table of FIG. 4.

[0057] As demonstrated by the results summarized in FIG. 4, the samplerotor hubs of Examples 1-4 exhibited superior corrosion resistance andno deposition of sulfur-containing particles, compared with that of theComparative Example. In addition, Examples 1 to 4 showed no substantialgeneration of sulfur-containing gas which generation would adverselyaffect the hard disk apparatus, thus offering a remarkable advantage.

[0058] 2. Passivation of Free Cutting Stainless Steel

[0059] In accordance with a second aspect of the present invention, thefree cutting stainless steel which has been prepared to meet theabove-described requirements, is machined into a desired shape and isthen subjected to a passivation treatment. As a result of suchtreatment, chemically active manganese sulfide, which may be present onor deposited to the surface of the stainless steel during machining, iseasily removed and any particle contamination which otherwise may becaused by the manganese sulfide is eliminated. This contributes toimprovement in corrosion resistance and suppression of contamination byparticles.

[0060] The passivation treatment effectively serves also to clean andremove rust from the surface of the stainless steel part. Morespecifically, chlorine contained in the cutting oil used duringmachining, as well as sulfur and scale which are formed in the course ofthe machining, are removed from the surface of the stainless steel part.As a result, the stainless steel part becomes more resistant tocorrosion.

[0061] The passivation treatment is preferably, but not exclusively,conducted with an aqueous solution of nitric acid alone. Althoughhydrogen sulfide (H₂S) is generated in the course of the passivationtreatment due to reaction between the nitric acid and sulfur compoundexisting in the stainless steel, such hydrogen sulfide can be removed byrinsing with water, hot water and finally with pure water conductedafter the passivation treatment. When using nitric acid alone, thefreeing of sulfur after the passivation treatment is reduced and can becompleted in a relatively short time.

[0062] The passivation treatment may also be conducted using as thetreating solution a mixture of nitric acid and sodium bichromate. Insuch treatment, the hydrogen sulfide generated as a result of thereaction between the nitric acid and the sulfur compound is oxidized bythe sodium bichromate, so as to free sulfur. It is, however, difficultto remove the sulfur thus freed by rinsing, which undesirably acts as asource of the corrosive sulfur gas. In addition to its facilitating theremoval of freed sulfur, corrosion by the acid is suppressed by virtueof the neutralizing, thus enhancing corrosion-resistance of thestainless steel.

[0063] The rate of generation of sulfur is, however, still lower withthe passivation solution composed of the mixture of nitric acid andsodium bichromate as compared with conventional steel materials. Thisresults from the free cutting stainless steel's smaller amount ofchemically active manganese sulfide. The sulfur, therefore, can beremoved without substantial difficulty by a subsequent neutralizingtreatment.

[0064] Such a neutralizing treatment may optionally be followed by achromate treatment, so that an oxide film is forcibly formed on thesurface of the stainless steel part, thus achieving a remarkableimprovement in corrosion resistance. It is noted that chromate treatmentwithout the prior alkali neutralizing treatment undesirably allowsgeneration of sulfur due to residual nitric acid or hydrogen sulfideadhering to the surface of the stainless steel part or in the pores fromwhich the free cutting element has been freed.

[0065] Following the passivation treatment, baking may optionally beconducted in place of the neutralizing treatment and the subsequentchromate treatment. Freed sulfur can be removed without difficulty bybaking, since the amount of sulfur is smaller than that of conventionalfree cutting stainless steels having the Mn/S ratio values of about 4.The baking serves to facilitate removal of acid and sulfur-containinggas on the surface of the stainless steel part, thus effectivelysuppressing contamination by particles.

[0066] The stainless steel which has undergone the passivation treatmentis heated at a temperature of from about 100° C. to 200° C. This heatingis effective not only in removing the sulfur gas remaining on thesurface of the stainless steel part, but also in forcibly releasing thepassivation solution, i.e., the acid. Preferably, the heating isconducted for a period of 10 hours or more. The heating may also beconducted in a vacuum or a substantially vacuum atmosphere. In such acase, the heating temperature may be set in a relatively low range offrom about 70° C. to 150° C.

[0067] Advantages of the above-described aspects of the presentinvention can be further appreciated in light of the following examples.

EXAMPLE 5

[0068] An 18 Cr stainless steel, having a sulfur content of 0.3 percentby mass and a manganese content of 0.4 percent by mass (Mn/Sratio=1.33), was prepared. This stainless steel was machined to formsamples of a rotor hub 40 shown in FIG. 3, i.e., the rotor hub whichforms part of a spindle motor and which is to be accommodated in theclean chamber of a hard disk apparatus.

[0069] Each sample of the rotor hub 40 thus formed was subjected to adegreasing treatment conducted with an alkali solution, and then to a40-minute passivation treatment conducted with a 50 percent by volumeaqueous solution of nitric acid at 50° C. This was followed by rinsingwith water, hot water and pure water and a subsequent dehydration by hotair. A silver plate, prepared by plating a stainless steel plate withsilver, was wound around each sample rotor hub which had undergone thepassivation treatment. The rotor hub together with the silver plate waswrapped in an aluminum foil and was shelved for 4 hours at 120° C. Thesilver plate was next separated, and a visual observation of the degreeof discoloration (silver plate color test) was conducted.

[0070] Twenty (20) pieces of the passivation treated rotor hub samples,were prepared and shelved for 360 hours in an 80° C. atmosphere of 90%humidity. Each piece of rotor hub was then subjected to opticalmicroscopic observation for any rusting.

[0071] A conductive tape was brought into contact with the surface ofeach of three pieces of the passivation treated sample rotor hubs. Fifty(50) arbitrarily selected particles of foreign matter transferred to thetape were analyzed through a scanning electron microscope/energydistribution X-ray analyzer (SEM/EDX), for the purpose of investigatingthe number of sulfur-containing particles. The results of thisevaluation are summarized in line a) of the table shown in FIG. 5.

COMPARATIVE EXAMPLE 2

[0072] Sample rotor hubs prepared as in Example 5 were directlysubjected to cleaning with methylene chloride, without passivationtreatment, and to a subsequent water rinse with the aid of a neutraldetergent. The rotor hubs thus treated were evaluated in the same manneras Example 5, to obtain the results shown in line b) of the table ofFIG. 5.

COMPARATIVE EXAMPLE 3

[0073] Samples rotor hubs prepared as in Example 5 were subjected to analkali degreasing, acid cleaning with dilute nitric acid, and then to apassivation treatment for 30 minutes at 50° C. in a liquid mixture of 25percent by volume nitric acid and 2.0 percent by weight sodiumbichromate. This was followed by rinsing with water, hot water and thenpure water, and a subsequent dehydration by hot air. The rotor hubsamples were then evaluated in the same manner as Example 5, to obtainthe results shown in line c) of the table of FIG. 5.

COMPARATIVE EXAMPLE 4

[0074] Sample rotor hubs were prepared as in Example 5, from an 18 Crstainless steel having a sulfur content of 0.3 percent by mass and amanganese content of 1.2 percent by mass (Mn/S=4.0). These sample rotorhubs were passivated in the same manner as described in ComparativeExample 2, and were evaluated in the same manner as Example 5, to obtainthe results shown in line d) of the table of FIG. 5.

EXAMPLE 6

[0075] Sample rotor hubs were subjected to the same passivationtreatment as in Comparative Example 3, with the liquid mixture of 25percent by volume nitric acid and 2.0 percent by weight sodiumbichromate. In this case, however, the passivated samples wereneutralized by being immersed in an 80° C., 20 percent by volume aqueoussolution of sodium hydroxide for 30 minutes, prior to rinsing withwater, hot water and then pure water. The rinsed samples were evaluatedin the same manner as Example 5, to obtain the results shown in line e)of the table of FIG. 5.

EXAMPLE 7

[0076] Sample rotor hubs were subjected to passivation andneutralization as in Example 6, and were chromate-treated by beingimmersed in a 70° C., 5 percent by weight aqueous solution of sodiumbichromate for 30 minutes. The samples after the chromate treatment wereevaluated in the same manner as Example 5, to obtain the results shownin line f) of the table of FIG. 5.

EXAMPLE 8

[0077] Sample rotor hubs were subjected to passivation as in ComparativeExample 3, followed by a 4-hour bake at 150° C. The samples wereevaluated in the same manner as Example 5, to obtain the results shownin line g) of the table of FIG. 5.

EXAMPLE 9

[0078] Sample rotor hubs were subjected to passivation as in ComparativeExample 3, followed by a 4-hour bake at 100° C. under a reduced pressureof 0.1 Torr. The samples were evaluated in the same manner as Example 5,to obtain the results shown in line h) of the table of FIG. 5.

COMPARATIVE EXAMPLE 5

[0079] Sample rotor hubs were subjected to passivation as in ComparativeExample 4, followed by a 4-hour bake at 150° C. The samples wereevaluated in the same manner as Example 5, to obtain the results shownin line i) of the table of FIG. 5.

COMPARATIVE EXAMPLE 6

[0080] Sample rotor hubs were subjected to passivation as in ComparativeExample 4, followed by a 4-hour bake at 100° C. under a reduced pressureof 0.1 Torr. The samples were evaluated in the same manner as Example 5,to obtain the results shown in line i) of the table of FIG. 5.

[0081] As demonstrated by the results summarized in FIG. 5, the samplerotor hubs of Examples 5-9 in accordance with the invention showed nosubstantial generation of sulfur-containing gas, which generation wouldadversely affect the hard disk apparatus. Examples 5-9 further show areduced rusting tendency and substantially no deposition ofsulfur-containing particles, in contrast to the Comparative Examples.

[0082] 3. Degreasing, Rust-Removing and Descaling of Free CuttingStainless Steel

[0083] In accordance with a third aspect of the present invention, thefree cutting stainless steel which has been prepared to meet theabove-described requirements, is machined into a desired shape and isthen subjected to a degreasing treatment. The degreasing treatment isconducted with a chlorine-type or hydrocarbon-type solvent, such asmethylene chloride, trichloroethylene, tetrachloroethylene or the likeor, alternatively, an alkali aqueous solution, such as sodium hydroxideor the like. The surface of the stainless steel part is cleaned as aresult of the degreasing treatment.

[0084] More specifically, the degreasing treatment effectively serves toremove chlorine and sulfur transferred from the machining oil during themachining, and dust and cuttings generated during the machining, as wellas micro-fine grains of free cutting components, such as sulfides. Thisdegreasing treatment alone, however, cannot completely remove scale,rust and particles residing in fine recesses of complicated machinedsurface, failing to ensure sufficiently high corrosion resistance.

[0085] Therefore, in accordance with this aspect of the invention, afterthe degreasing treatment, the stainless steel part is subjected to achemical treatment for rust removal and descaling. This rust-removing,descaling chemical treatment may be effected by electrolytic cleaning,using an aqueous solution of an acid, such as nitric acid, sulfuricacid, hydrochloric acid or the like, or an aqueous solution of an alkalisuch as sodium hydroxide, potassium hydroxide, sodium silicate, sodiumphosphate, sodium gluconate or the like. The contaminant, scale andparticles can be removed almost completely by this chemicalrust-removing, descaling treatment, whereby high corrosion resistancepeculiar to the stainless steel can be fully utilized and contaminationby particles avoided.

[0086] The rust-removing, descaling treatment may be conducted underrelatively gentle conditions, whichever one of the aforementionedtechniques is employed. Use of a stainless steel having amanganese-to-sulfur ratio Mn/S of 1.8 or less enhances generation ofchemically stable CrS, thus contributing to generation of H₂S throughthe rust-removing, descaling chemical treatment. However, generation ofsulfur-containing gas is observed even with this type of stainless steelwhen the treatment is conducted by employing a commonly used acidsolution having an acid concentration of 15 percent by volume or higher.This is because such an acid solution dissolves the chemically stableCrS. It is, therefore, preferred that the rust-removing, descalingchemical treatment be conducted with an aqueous solution of an acidhaving an acid concentration of 3 percent by volume or less. Thestainless steel which has undergone the rust-removing, descalingchemical treatment described above, exhibits improved corrosionresistance and reduced particle contamination.

[0087] A further improvement in the corrosion resistance is achievableby effecting an optional chromate treatment on the stainless steel whichhas undergone the rust-removing, descaling chemical treatment. Such achromate treatment forcibly forms an oxide film on the surface of thestainless steel part, thereby remarkably enhancing resistance tocorrosion.

[0088] Advantages of the above-described aspects of the presentinvention can be further appreciated in light of the following examples.

EXAMPLE 10

[0089] An 18 Cr stainless steel, having a sulfur content of 0.3 percentby mass and a manganese content of 0.4 percent by mass (Mn/Sratio=1.33), was prepared. This stainless steel was machined to formsamples of a rotor hub 40 shown in FIG. 3, i.e., the rotor hub whichforms part of a spindle motor and which is to be accommodated in theclean chamber of a hard disk apparatus.

[0090] Each sample of the rotor hub 40 thus formed was subjected to adegreasing process, conducted using methylene chloride and sodiumhydroxide. Each of the samples was then subjected to a rust-removing,descaling chemical treatment conducted by immersing the rotor hubs in a2 percent by volume aqueous solution of hydrochloric acid of roomtemperature for 3 minutes. The rotor hub samples were then rinsed withwater, pure hot water and pure water, followed by a hot-air dehydration.Each sample thus treated was placed in a sealable 100 ml container,together with a silver plate (stainless steel sheet plated with silver).

[0091] Each container was then hermetically sealed after dripping two orthree droplets of pure water into the container, and was shelved for 12hours in a 90° C. atmosphere. The silver plate was then taken out of thecontainer for visual observation of the degree of discoloration (silverplate color test).

[0092] Twenty (20) pieces of such rotor hub samples, having undergonethe rust-removing descaling treatment, were shelved for 360 hours in an80° C. atmosphere of 90% humidity. Each piece of rotor hub was thensubjected to optical microscopic observation for any rusting.

[0093] A conductive tape was brought into contact with the surface ofeach of three pieces of the sample rotor hubs which had undergone therust-removing, descaling chemical treatment. Fifty (50) arbitrarilyselected particles of foreign matter transferred to the tape wereanalyzed through a scanning electron microscope/energy distributionX-ray analyzer (SEM/EDX), for the purpose of investigating the number ofsulfur-containing particles. The results of this evaluation aresummarized in line a) of the table shown in FIG. 6.

EXAMPLE 11

[0094] Sample rotor hubs prepared in Example 10 were subjected to analkali degreasing treatment and then to an electrolytic cleaning, inwhich each sample rotor hub was connected to anode and held for 2minutes in an alkali aqueous solution containing 3 percent by volume oforthosodium silicate, 2 percent by volume of sodium hydroxide and 2percent by volume of sodium carbonate. The sample rotor hubs were thenrinsed with water, hot pure water and pure water, followed bydehydration with hot air. The sample rotor hubs thus treated wereevaluated to obtain the results shown in line b) of the table of FIG. 6.

EXAMPLE 12

[0095] The sample rotor hubs which underwent the electrolytic cleaningin Example 11 were then subjected to a chromate treatment, in which thesample rotor hubs were immersed in a 5 percent by weight aqueoussolution of sodium bichromate at 70° C. for 30 minutes. Evaluation wasconducted in the same manner as in the preceding Examples, to obtain theresults shown in line c) of the table of FIG. 6.

EXAMPLE 13

[0096] The sample rotor hubs prepared in Example 10 were immersed for 20minutes in a 50 percent by volume solution of nitric acid of the normaltemperature for rust removal and descaling, followed by rinsing withwater, pure hot water and pure water and a subsequent dehydration.Evaluation was conducted in the same manner as in the precedingExamples, to obtain the results shown in line d) of the table of FIG. 6.

COMPARATIVE EXAMPLE 7

[0097] Sample rotor hubs were prepared by machining an 18 Cr stainlesssteel having a sulfur content of 0.3 percent by mass and a manganesecontent of 1.2 percent by mass (Mn/S=4), and by subjecting them to thesame treatment described above with reference to Example 10. Evaluationwas conducted in the same manner as in the preceding Examples, to obtainthe results shown in line e) of the table of FIG. 6.

COMPARATIVE EXAMPLE 8

[0098] Sample rotor hubs were prepared by machining an 18 Cr stainlesssteel having a sulfur content of 0.3 percent by mass and a manganesecontent of 1.2 percent by mass (Mn/S=4), and by subjecting them to thesame treatment described above with reference to Example 11. Evaluationwas conducted in the same manner as in the preceding Examples, to obtainthe results shown in line f) of the table of FIG. 6.

COMPARATIVE EXAMPLE 9

[0099] Sample rotor hub 40 having a configuration as shown in FIG. 3 wasprepared by machining an 18 Cr stainless steel having a sulfur contentof 0.3 percent by mass and a manganese content of 1.2 percent by mass(Mn/S=4), and then rinsing with methylene chloride. Evaluation wasconducted in the same manner as in the preceding Examples, to obtain theresults shown in line g) of the table of FIG. 6.

[0100] As clearly demonstrated by the results shown in FIG. 6, thesample rotor hubs of Examples 10-13 showed no or only a slight change incolor of the silver plates caused by sulfur-containing gas, as comparedwith the sample rotor hubs of Comparative Examples 7-9, thusdemonstrating improved corrosion resistance. In addition, Examples 10-13showed no substantial generation of sulfur-containing gas whichgeneration would adversely affect the hard disk apparatus, thus offeringa remarkable advantage.

[0101] 4. Degreasing and Chromate Treatment of Free Cutting StainlessSteel

[0102] In accordance with a further aspect of the present invention, thefree cutting stainless steel which has been prepared to meet theabove-described requirements, is subjected to a degreasing andsubsequent chromate treatment. As described above, the chromatetreatment forcibly forms an oxide film on the surface of the stainlesssteel, thereby especially improving resistance to corrosion withoutinfluence of the generation of the sulfur-containing corrosive gas andof the dissolution of the free cutting components on the surface of thesteel material. To further improve the resistance to corrosion, the freecutting stainless steel can optionally be subjected to mechanicaldescaling before the degreasing.

[0103] The advantages of this aspect of the present invention will beapparent from the following examples.

EXAMPLE 18

[0104] Sample rotor hubs prepared in Example 10 were subjected to analkali degreasing treatment and were then subjected to a chromatetreatment in which the sample rotor hubs were immersed in a 5 percent byweight aqueous solution of sodium bichromate at 70° C. for 30 minutes.Evaluation was conducted in the same manner as in the precedingExamples, to obtain the results shown in line h) of the table of FIG. 6.

EXAMPLE 19

[0105] Sample rotor hubs prepared in Example 10 were subjected torinsing with ethylene oxide, and were then the whole of the diskmounting surface was buffed. The sample rotor hubs were subsequentlysubjected to a degreasing treatment, and were evaluated in the samemanner as in the preceding Examples, to obtain the results shown in linei) of the table of FIG. 6.

[0106] The results shown in FIG. 6 demonstrate that the sample rotorhubs of Examples 18 and 19 showed no change in color of the silverplates caused by sulfur-containing gas, as compared with the samplerotor hubs of Comparative Examples 6-8, thus demonstrating improvedcorrosion resistance. In addition, Examples 18 and 19 showed nosubstantial generation of sulfur-containing gas which generation wouldadversely affect the hard disk apparatus, thus offering a remarkableadvantage.

[0107] Although the invention has been described in terms of practicalembodiments, it is to be understood that the described embodiments areonly illustrative, and various modifications and changes may be impartedwithout departing from the spirit and scope of the present invention.

What is claimed is:
 1. A hard disk apparatus, comprising: a cleanchamber accommodating a hard disk driven by a spindle motor, and amagnetic head capable of making access to said hard disk, wherein a freecutting stainless steel is used as the material of a member accommodatedin said clean chamber, said free cutting stainless steel having a sulfur(S) content of not less than 0.25 percent by mass and amanganese-to-sulfur content ratio (Mn/S) of not greater than 1.8, saidfree cutting stainless steel having been subjected to an acid cleaning.2. The hard disk apparatus according to claim 1 , wherein the acidcleaning is conducted with a treating solution which is an aqueoussolution of an acid effective to remove contaminants, rust and scaleremaining on the surface of the free cutting stainless steel.
 3. Thehard disk apparatus according to claim 1 , wherein the acid cleaning isconducted with a treating solution comprising nitric acid.
 4. The harddisk apparatus according to claim 1 , wherein following the acidcleaning, the free cutting stainless steel is subjected to aneutralizing treatment and a chromate treatment.
 5. The hard diskapparatus according to claim 1 , wherein said component is a rotor hubof said spindle motor.
 6. A hard disk apparatus, comprising: a cleanchamber accommodating a hard disk driven by a spindle motor, and amagnetic head capable of making access to said hard disk, wherein a freecutting stainless steel is used as the material of a member accommodatedin said clean chamber, said free cutting stainless steel having a sulfur(S) content of not less than 0.25 percent by mass and amanganese-to-sulfur content ratio (Mn/S) of not greater than 1.8, saidfree cutting stainless steel having been subjected to a passivationtreatment.
 7. The hard disk apparatus according to claim 6 , wherein thepassivation treatment is conducted with a nitric acid treating solution.8. The hard disk apparatus according to claim 6 , wherein thepassivation treatment is conducted with a treating solution which is amixture of nitric acid and sodium bichromate, and wherein an alkalineutralizing treatment is conducted after the passivation treatment. 9.The hard disk apparatus according to claim 8 , wherein a chromatetreatment is conducted after the alkali neutralizing treatment.
 10. Thehard disk apparatus according to claim 6 , wherein said free cuttingstainless steel is heat-treated at a temperature of from about 100° C.to about 200° C. after the passivation treatment.
 11. The hard diskapparatus according to claim 6 , wherein said free cutting stainlesssteel is heat-treated at a temperature of from about 70° C. to about150° C. in a vacuum or a substantially vacuum atmosphere after thepassivation treatment.
 12. The hard disk apparatus according to claim 6, wherein said member is a rotor hub of said spindle motor.
 13. A harddisk apparatus, comprising: a clean chamber accommodating a hard diskdriven by a spindle motor, and a magnetic head capable of making accessto said hard disk, wherein a free cutting stainless steel is used as thematerial of a member accommodated in said clean chamber, said freecutting stainless steel having a sulfur (S) content of not less than0.25 percent by mass and a manganese-to-sulfur content ratio (Mn/S) ofnot greater than 1.8, said free cutting stainless steel having beensubjected to a degreasing treatment and to a subsequent rust-removing,descaling chemical treatment.
 14. The hard disk apparatus according toclaim 13 , wherein the rust-removing, descaling chemical treatment isconducted with a treating solution which is an aqueous solution of anacid having an acid concentration of 3 percent by volume or less. 15.The hard disk apparatus according to claim 13 , wherein therust-removing, descaling chemical treatment comprises an alkalielectrolytic cleaning.
 16. The hard disk apparatus according to claims13, wherein following the rust-removing, descaling chemical treatmentsaid free cutting stainless steel is subjected to a chromate treatment.17. The hard disk apparatus according to claim 13 , wherein said memberis a rotor hub of said spindle motor.
 18. A hard disk apparatus,comprising: a clean chamber accommodating a hard disk driven by aspindle motor, and a magnetic head capable of making access to said harddisk, wherein a free cutting stainless steel is used as the material ofa member accommodated in said clean chamber, said free cutting stainlesssteel having a sulfur (S) content of not less than 0.25 percent by massand a manganese-to-sulfur content ratio (Mn/S) of not greater than 1.8,said free cutting stainless steel having been subjected to a degreasingtreatment and to a subsequent chromate treatment.
 19. The hard diskapparatus according to claim 18 , wherein prior to the degreasingtreatment, the free cutting stainless steel is subjected to a mechanicaldescaling treatment.
 20. The hard disk apparatus according to claim 18 ,wherein said member is a rotor hub of said spindle motor.
 21. A datastorage device, comprising a clean chamber accommodating a component,said component being formed from a free cutting stainless steel, saidfree cutting stainless steel having a sulfur (S) content of not lessthan 0.25 percent by mass and a manganese-to-sulfur content ratio (Mn/S)of not greater than 1.8, said free cutting stainless steel having beensubjected to an acid cleaning.
 22. The data storage device according toclaim 21 , wherein the acid cleaning is conducted with a treatingsolution which is an aqueous solution of an acid effective to removecontaminants, rust and scale remaining on the surface of the freecutting stainless steel.
 23. The data storage device according to claim21 , wherein the acid cleaning is conducted with a treating solutioncomprising nitric acid.
 24. The data storage device according to claim21 , wherein following the acid cleaning, the free cutting stainlesssteel is subjected to a neutralizing treatment and a chromate treatment.25. The data storage device according to claim 21 , wherein a spindlemotor is accommodated in the clean chamber for driving one or more datastorage media, and a rotor hub of said spindle motor constitutes a partof said component.
 26. A data storage device, comprising a clean chamberaccommodating a component, said component being formed from a freecutting stainless steel, said free cutting stainless steel having asulfur (S) content of not less than 0.25 percent by mass and amanganese-to-sulfur content ratio (Mn/S) of not greater than 1.8, saidfree cutting stainless steel having been subjected to a passivationtreatment.
 27. The data storage device according to claim 26 , whereinthe passivation treatment is conducted with a nitric acid treatingsolution.
 28. The data storage device according to claim 26 , whereinthe passivation treatment is conducted with a treating solution which isa mixture of nitric acid and sodium bichromate, and wherein an alkalineutralizing treatment is conducted after the passivation treatment. 29.The data storage device according to claim 27 , wherein a chromatetreatment is conducted after the alkali neutralizing treatment.
 30. Thedata storage device according to claim 26 , wherein said free cuttingstainless steel is heat-treated at a temperature of from about 100° C.to about 200° C. after the passivation treatment.
 31. The data storagedevice according to claim 26 , wherein said free cutting stainless steelis heat-treated at a temperature of from about 70° C. to about 150° C.in a vacuum or a substantially vacuum atmosphere after the passivationtreatment.
 32. The data storage device according to claim 26 , wherein aspindle motor is accommodated in the clean chamber for driving one ormore data storage media, and a rotor hub of said spindle motorconstitutes a part of said component.
 33. A data storage device,comprising a clean chamber accommodating a component, said componentbeing formed from a free cutting stainless steel, said free cuttingstainless steel having a sulfur (S) content of not less than 0.25percent by mass and a manganese-to-sulfur content ratio (Mn/S) of notgreater than 1.8, said free cutting stainless steel having beensubjected to a degreasing treatment and to a subsequent rust-removing,descaling chemical treatment.
 34. The data storage device according toclaim 33 , wherein the rust-removing, descaling chemical treatment isconducted with a treating solution which is an aqueous solution of anacid having an acid concentration of 3 percent by volume or less. 35.The data storage device according to claim 33 , wherein therust-removing, descaling chemical treatment comprises an alkalielectrolytic cleaning.
 36. The data storage device according to claim 33, wherein following the rust-removing, descaling chemical treatment,said free cutting stainless steel is subjected to a chromate treatment.37. The data storage device according to claim 33 , wherein a spindlemotor is accommodated in the clean chamber for driving one or more datastorage media, and a rotor hub of said spindle motor constitutes a partof said component.
 38. A data storage device, comprising a clean chamberaccommodating a component, said component being formed from a freecutting stainless steel, said free cutting stainless steel having asulfur (S) content of not less than 0.25 percent by mass and amanganese-to-sulfur content ratio (Mn/S) of not greater than 1.8, saidfree cutting stainless steel having been subjected to a degreasingtreatment and to a subsequent chromate treatment.
 39. The data storagedevice according to claim 38 , wherein prior to the degreasingtreatment, the free cutting stainless steel is subjected to a mechanicaldescaling treatment.
 40. The data storage device according to claim 38 ,wherein a spindle motor is accommodated in the clean chamber for drivingone or more data storage media, and a rotor hub of said spindle motorconstitutes a part of said component.